Otitis media (OM) is a highly prevalent pediatric disease worldwide and is the primary cause for emergency room visits by children (Infante-Rivand and Fernandez, Epidemiol. Rev., 15: 444-465, 1993). Recent statistics indicate that 24.5 million physician office visits were made for OM in 1990, representing a greater than 200% increase over those reported in the 1980's. While rarely associated with mortality any longer, the morbidity associated with OM is significant. Hearing loss is a common problem associated with this disease, often times affecting a child's behavior, education and development of language skills (Baldwin, Am. J. Otol., 14: 601-604, 1993; Hunter et al., Ann. Otol. Rhinol. Laryngol. Suppl., 163: 59-61, 1994; Teele et al., J. Infect. Dis., 162: 685-694, 1990). The socioeconomic impact of OM is also great, with direct and indirect costs of diagnosing and managing OM exceeding $5 billion annually in the U.S. alone (Kaplan et al., Pediatr. Infect. Dis. 16: S9-11, 1997).
Whereas antibiotic therapy is common and the surgical placement of tympanostomy tubes has been successful in terms of draining effusions, clearing infection and relieving pain associated with the accumulation of fluids in the middle ear, the emergence of multiple antibiotic-resistant bacteria and the invasive nature associated with tube placement, has illuminated the need for more effective and accepted approaches to the management and preferably, the prevention of OM. Surgical management of chronic OM involves the insertion of tympanostomy tubes through the tympanic membrane while a child is under general anesthesia. While this procedure is commonplace (prevalence rates are ˜13%; Bright et al., Am. J. Public Health, 83(7): 1026-8, 1993) and is highly effective in terms of relieving painful symptoms by draining the middle ear of accumulated fluids, it too has met with criticism due to the invasive nature of the procedure and its incumbent risks (Berman et al., Pediatrics, 93(3):353-63, 1994; Bright et al., supra.; Cimons, ASM News, 60: 527-528; Paap, Ann. Pharmacother., 30(11): 1291-7, 1996).
Progress in vaccine development is most advanced for Streptococcus pneumoniae, the primary causative agent of acute OM (AOM), as evidenced by the recent approval and release of a seven-valent capsular-conjugate vaccine, PREVNAR® (Eskola and Kilpi, Pedriatr. Infect. Dis. J. 16: S72-78, 2000). While PREVNAR® has been highly efficacious for invasive pneumococcal disease, coverage for OM has been disappointing (6-8%) with reports of an increased number of OM cases due to serotypes not included in the vaccine (Black et al., Pedriatr. Infect. Dis J., 19: 187-195; Eskola et al., Pedriatr. Infect. Dis 1, 19: S72-78, 2000; Eskola et al., N. Engl. J. Med. 344: 403-409, 2001; Snow et al., Otol. Neurotol., 23: 1-2, 2002). Less progress has been made for non-typeable Haemophilus influenzae (NTHi), the gram-negative pathogen that predominates in chronic OM with effusion (Klein, Pedriatr. Infect. Dis J., 16: S5-8, 1997; Spinola et al., J. Infect. Dis., 154: 100-109, 1986). Hampering development of effective vaccines against NTHi, is the currently incomplete understanding of the pathogenesis of NTHi-induced middle ear disease. Contributing to this delay is a lack of understanding of the dynamic interplay between microbe-expressed virulence factors and the host's immune response as the disease progresses from one of host immunological tolerance of a benign nasopharyngeal commensal, to that of an active defensive reaction to an opportunistic invader of the normally sterile middle ear space.
Although strain Rd is the exemplar organism for the current small genome sequencing rationale, and an important model organism for studying H. influenzae biology, strain Rd is a poor model for the study of pathogenicity caused by members of the genus Haemophilus. Serotype b strains of H. influenzae cause invasive diseases, for example meningitis, and nontypeable H. influenzae (NTHi) strains principally have a role in localized respiratory disease, particularly in otitis media (OM), acute sinusitis, community acquired pneumonia and have important consequences in patients with chronic obstructive pulmonary disease or cystic fibrosis (Kilpi et al., Pediatr Infect Dis J 20:654-62, 2001; Murphy, Curr Opin Infect Dis 16:129-34, 2003; Roman et al., J Clin Microbial 42:1450-9, 2004; Sethi, Clin Microbiol Rev 14:336-63, 2001; St Geme, Vaccine 19 Suppl 1:S41-50, 2000). Strain Rd, however, is a derivative of a serotype d strain. Serotype d strains are rarely associated with disease (Daines et at, J Med Microbiol 52:277-82 2003; Heath et al., Pediatr Infect Dis J 20:300-5, 2001; Rodriguez et al., Infect Immun 71:1635-42, 2003, Skoczynska et al., J Clin Microbiol 43:938-41, 2005). Because one of the most useful sets of data in the study of an organism's biology is its genomic sequence, a number of investigations have identified and characterized genes found in H. influenzae type b strains, H. influenzae Biogroup Aegyptius strains or in nontypeable strains that are not present in strain Rd (Bergman et al., Infect Immun 71:1098-108, 2003; Chang et al., Infect Immun 68:2630-7, 2000; Erdos et al., Int J Pediatr Otorhinolaryngol 67:749-55. 2003; Li et al., Mol Microbiol 47:1101-11, 2003; McMichael & Green, Curr Opin Investig Drugs 4:953-8, 2003; Pomposiello & Demple, 2001; Smoot et al., Infect Immun 70:2694-9, 2002).
Currently there is a poor understanding of how NTHi causes OM in children. The identification of putative virulence factors necessary for induction of OM will contribute significantly to the understanding of the host-pathogen interaction and ultimately, the identification of potential vaccine candidates and targets of chemotherapy. There is a tremendous need to develop more effective and accepted approaches to the management and preferably, the prevention of otitis media. Vaccine development is a very promising and cost effective method to accomplish this goal (Giebank, Pedriatr. Infect. Dis J., 13(11): 1064-8, 1994: Karma et al., Int. J. Pedritr. Otorhinolalyngol., 32(Suppl.): S127-34, 1995).